The present invention relates to a fuel injection system for an externally ignited internal combustion engine which operates on fuel which is continuously injected into the suction tube in which a sensor element and an arbitrarily operable butterfly valve are disposed in series. The sensor element is moved by and in proportion to the quantity of air flowing through the pipe against a restoring force. In the course of its excursion, the sensor element displaces a movable component of a valve disposed in the fuel supply line for metering a proportionate quantity of fuel to air. The afore-mentioned restoring force is supplied by liquid under pressure which is delivered continuously under constant, but arbitrarily variable pressure through a control pressure line and which exerts a force on a control plunger transferring the restoring force. The pressure of said liquid is variable by at least one pressure control valve controllable as a function of the engine parameters. The pressure control valve is in the form of a flat seat valve comprising a valve membrane as the movable valve part.
Fuel injection systems of this type are designed to automatically provide a good fuel-air mixture for all operating conditions of the internal combustion engine so as to burn the fuel as completely as possible and thus while obtaining maximum performance of the internal combustion engine, with minimum fuel consumption, to prevent toxic exhaust gases from being produced, or at least to reduce considerably the same. The quantity of fuel, therefore, must be metered very accurately in accordance with the requirements of each operational state of the internal combustion engine.
In the case of known fuel injection systems of this type, the quantity of fuel which is metered is, as far as possible, proportionate to the quantity of air flowing through the suction tube. The ratio of the quantity of fuel which is metered to the quantity of air may be varied by changing the restoring force of the sensing element as a function of the operating parameters by means of an electromagnetically actuated pressure control valve.
It has been found that it is advantageous to momentarily enrich the fuel-air mixture when the throttle valve (butterfly valve) is suddenly opened and to weaken momentarily the fuel-air mixture when the throttle valve is suddenly closed.